A structure fire at an abandoned Eureka building on Monday morning that created a cloud of black smoke over the city and snarled traffic in the downtown area has been deemed suspicious by Humboldt Bay Fire.

The fire happened around 10 a.m. on the 400 block of Broadway Street at a building that used to be a hydraulics shop but has been vacant for several years. Three engines, a ladder truck and four chief officers responded to the scene. Humboldt Bay Fire Chief Bill Gillespie said there were no injuries, but he estimates property damage for the building itself is $40,000 and the structure is being torn down by a contractor that the owner has brought in.

"The walls are being pulled down because the structure is now a safety hazard. The fire investigation is ongoing, but we are deeming it suspicious at this time because it's an unoccupied building and there are no real ignition points," Gillespie said. "Crews weren't able to go in and investigate extensively because there was quite a bit of the roof structure coming down and it was too unstable."

During the incident, a neighboring billboard caught on fire. Power lines surrounding the structure fell down and Pacific Gas and Electric Company officials were called to the scene to make sure service had been disconnected.

"The building next door sustained some heat damage," Gillespie said. "Some blinds on the inside of the building melted and some windows cracked from the heat. We had crews inside the building to make sure the fire didn't spread there, because sometimes it can just from radiant warmth."

Gillespie said around 1 p.m., while the property owner was still on the scene after the fire had been extinguished, a few embers in the front of the building began to flare up.

"There was a small, smoldering fire where the roof and front wall came together that crews extinguished," Gillespie said. "We've responded to that location on and off throughout the years while it has been a vacant structure. Fires have been caused there by transient people either staying inside the building or using cooking or warming fires outside the building."

Eureka's Chief Building Official Brian Gerving said the city has been working with the property owner of the building over the past several months to either repair or demolish the structure because of the damaged state it was in due to previous fires.

"As a result of the damage done by the fire (on Monday), demolishing the structure had to be done immediately," Gerving said.

It was the second fire of the morning in Eureka.

A fire at a homeless encampment at the north end of the Bayshore Mall was put out by Humboldt Bay Fire around 8:30 a.m.

Humboldt Bay Fire Capt. Brooks Conner said the cause is unknown and no one was injured.

"We aren't sure whether it was an accident or retaliation," Conner said. "All the belongings and tarps had burned when we got there, and there were no people. It took 15 minutes and 500 gallons of water to fully extinguish the fire."